Method of producing metals having radioactivity



Aug. 26, 1941. J. H. DILLON 2,254,170

METHOD OF rnonucme METALS mvme RADIOACTIVITY Filed Jan. 4, 1940 2Sheets-Sheet 1 INVENTOR JOHN H. DILLON ATTORNEYS Aug. 26, 1941.

J. H. DILLON METHOD OF PRODUCING METALS HAVING RADIOACTIVITY SEPARATINGRADIUM D AND Filed Jan. 4, 1940 TREATING RADIUM D- LEAD RESIDUE TOPRODUCE RADIUM D AND LEAD CHLORI DES AGING RADIUM D AND LEAD CHLORIDES 2Sheets-Sheet 2 LEAD CHLORIDES TITRATI NG MOTHER LIQUOR TO 0.03 NORMALHYDROCHLORIC TO D EVELOP POLONIUM ADDING- AGED RADIUM D POLONIUM ANDLEAD CHLORIDES TO TITRATED LIQUOR PREPARING LIQUOR OFAGED RADIUM DPOLONIUM AN-D LEAD CHLORIDES RADIUM D AND LEAD CHLORIDES ALLOVING FOILACID I I T COOLINGS PENT PLATING POLONIUM PREPARING- FOILPLATINGSOLUTION ON FOIL FOR PLATING' TO PRECIPITATE INCREASE IN POLONIUMCONTENT OF RADIUM D COMPOSITION RATIO OF POLONIUM TO INITIAL RADIUM 0ELAPSED TIME IN DAYS INVENTOR (JOHN H. DILLON ATTORNEYS Patented Aug.26, 1941 UNITED STATES. PATENT OFFICE METHOD OF PRODUCING METALS HAVINGRADIOAUIIVITY John H, Dillon, Akron, Ohio, assignor to The FirestoneTire .1; Rubber Company, Akron. Ohio, a corporation of Ohio ApplicationJanuary 4, 1940, Serial No. 313,441

12 Claims.

This invention relates especially to polonium alloys and method ofpreparing same, but it also to, provide a practical method of making aradio-- active alloy, by the operation of which the amount ofradioactive metal in the finished alloy may be readily, controlled.

Another primary object is to provide a radio- 7 active alloy resultingfrom said method.

Another, object is to provide a method of mak- 7 ing a polonium alloy.

. Another object is to provide a method of making a radioactive alloycomprising nickel or, specifically, a nickel-polonium alloy.

Another object is to provide a radioactive alloy comprising a small butdefinite proportion of I determinations. (See 1:. Walling, Zeitschriftfiir jPhyslk, av, 003 (1934) a radioactive metal.

' A further object is to devise a commercially practical method ofproducing metallic from its salts. v

Further objects will be manifest from the specification, reference beinghad to theaccompanylng drawings, in which:

Figure 1 is an elevation, partly in section, of apparatus suitable forcarrying out thepreferred process of the presentinvention;

Figure 2 is a flow-sheet of one embodiment oi the invention; and

'Figure 3 law diagrammatic representation of diiilculty from their ores,which are quite rare. However, it has been discovered that an alloycontaining an exceedingly small proportion of a strongly radioactivemetal possesses radioactive properties adequate for many purposes.

All radioactive materials give 01! one or more of three types ofradiation called alpha, beta and gamma rays. The alpha rays, which arerapidly moving, doubly charged particles, are much more emcient forcertain practical purposes, such as for ionizing gases, than either thebeta rays (fast electrons) or gamma rays (electromagnetic radiation ofextremely high frequency). Furtherd more, the alpha rays are notdangerous to human a harmful and require extreme safety precautions.-The'.beta rays are also dangerous to some extent.

beings, whereas gamma rays may be exceedingly Hence, it is quiteapparent that a radioactive material emitting only alpha rays is much tobe preferred for certain commercial purposes.

'Table I shows the important relationships existing among members of theuranium-radium series of radioactive elements, including the types ofrays given off. (See J. Am. Chem. Soc

the development of polonium by aging of .40

radium D. Broadly, the present invention comprises plating a thin filmof a radioactive metal onto thesurface of another metal, preferablyinfoil form. to produce a plated metal. The" plated metal is then meltedwith or without admixture of a dilutin'g metal to form an alloy of theradioactive metal having a predetermined degree of radioactivity, oramount of a radioactive metal associated therewith. The diluting metaland the metal'onto which the radioactive metal is plated are bothusually non-radioactive, although not necessarily so.

In general, radioactive metals are very ex- 45, 872 (1923).) The halflife value for radium D has been corrected to agree with more recentmeans radiation is relatively feeble.

don tubes, which are no longer suited for their p nsive' ause th y axtract d with a eal original therapeutic functions, constitute a con-Table 1 Atomic 7 Half life Radiation Wt. No.-

92 4.67X10' yrs... Alpha. 90 Beta. 91 Beta (gamma). 92 Al ha. 00 o. t 88Alphrflaeta and gamma Algha. Bi o. I 82 Beta (gamma). 83 Beta'and gamma84 Alpha. 82 22. (Beta and gamma).

83' 5.0days Beta. Si 136 days Alpha (gamma).

venient source of polonium. Radon tubes are small ampules of glass orgold originally charged with the gaseous radon evolved by radium salts.The radon changes into short-lived radium C, which gives oil powerfulgamma rays and makes the radon tubes medicinally useful. After a fewdays of usefulness by virtue of the gamma ray emission the radon tubesare medicinally spent," since they contain practically no radon orradium C. They now contain mainly the relatively stable solid radium D,which exists as a minute deposit on the inner walls of the tubes. Afterseveral months of aging an appreciable amount of polonium is containedin the tubes, formed from the radium D at the rate indicated by Figure3. Another source of greater commercial importance is the lead residueremaining after the extraction of radium from its ore. The lead residueis preferably treated to form the lead chloride salt. The resulting leadchloride contains all radioactive materials below radium C in the abovetable, being rich in radium D (an isotope of lead), which slowly changesinto radium E, and containing appreciable radium F, or polonium. RadiumE rapidly changes into polonium, as shown in the above table. Poloniumis of especial interest because it is the only known radioactive metalemitting the desirable alpha rays almost exclusively and at a practicalrate and glvingrlse to no other radioactive element emitting undesiredbeta or gamma rays. The immediate transformation product ofpolonium,radium omega, is an inactive isotope of ordinary lead. Thus no dangerousproducts develop from polonium, in contrast with radium, certaintransformation products of the latter emitting strong beta and gammaradiation. Table I indicates that polonium emits feeble gamma rays inaddition to strong alpha rays. It is well known that polonium emits onlya few quanta of gamma rays for each million alpha rays. (Sec II. C.Webster, Chemical Abstracts, 32, 1565-6 (1938).) Practically speaking,therefore, polonium emits only alpha rays.

In selecting a radioactive metal for use in preparing a practicalradioactive alloy the radiation activity of the metal must beconsidered. A radioactive element changes into another element accordingto an exponential law governed by the activity (number of rays persecond) of the element. The selection of a metal of very low activity,such as uranium, would be unwise, because, even though it has the longhalf life (time required for one mass unit of the substance to bereduced to one-half mass unit) of approximately five billion years andemits onlythe desirable alpha rays, the activity of even the pure metalis too low to be of any practical value. On the other hand, radium Aemits only alpha rays very copiously but has a half life of only threeminutes. Polonium emits alpha rays at a rate in excess of 4500 times thealpha emission rate of pure radium, and has the reasonable half life of136 days,-which period of time is suflicient in many cases for theutilization of the strong alpha radiation of the substances It ispracticable to add sufllcient polonium to an alloy such that the alloyhas useful radioactivity for many purposes several years after it isproduced. Only a very minute quantity of polonium need be present in analloy in order to render same ofspractical value. For example, a sparkplug electrode alloy initially containingas little as twoone-hundredengine, at the end of two years. when the polonium content ofthe alloy has fallen to less than one-billionth of one per cent.

Although polonium is the preferred radioactive metal for use in thepresent invention for the reasons given above, any other radioactivemetal may be employed, so far as the present method is concerned. Inaddition to-polonium certain other strongly radioactive metals emitalpha rays at effective rates and have sufliciently long halflifeperiods to render them especially useful in alloys. Such other stronglyradioactive metals are radium, radiothorium, protoactinium,radioactinium and actinium X. It would be necessary to handle an alloycontaining one of these metals with proper precautions in view of thebeta and gamma radiation attending the desired alpha ray emission. Ametal having an induced radioactivity is also contemplated for use inthe present invention.

The method of the present invention is unique, in that it may be used toprepare a radioactive alloy comprising an exceedingly low but definiteproportion of a radioactive metal. According to the present process theradioactive metal is first plated (by electrodeposition, electrochemicaldisplacement, adsorption or vaporization) onto a base metal (in anyconvenient form such as, for example, plate, foil, wire, granules orpowder). After determining the amount of plated radioactive metal, whichamount can be relatively accurately predetermined, by any suitablemeasurement, as hereinafter described, the plated object is then meltedwith or without admixture of further base metal or other metal in orderto produce the desired alloy or mixture of metals.

Unweighable quantities of the radioactive substance to be alloyed may bemeasured by a combination of an electroscope and an ionization chamberwhich has previously been calibrated against a known amount of aradioactive substance or an absolute measuring apparatus. An example 'ofthe latter type of apparatus is the so-called Geiger counter, such aswas described 5 by Rutherford and Geiger in The Proceedings of the RoyalSociety, volume 811A, pa e'141 (1908). Both of the above mentioneddevices are usually responsive to alpha, beta and gamma rays to agreater or less extent, but may be made responsive only to alpha rays byselection of appropriate conditions, even though other rays are present.By the use of such modifications these devices may be used to determineaccurately such an. alpha ray emitting substance as polonium, eventhough radioactive substances which emit' rays other than alpha are alsopresent.

The following specific examples of methods for obtaining a plating ofpolonium and for making the polonium-base metal alloys are given forillustrative purposes only and are not to be construed as limiting theinvention thereto:

Method A inch nickel foil (total surface area is 27,090

square millimeters) was etched the desired amount by treating it withconcentrated nitric acid and then was copper-plated in a coppersulfatesolution (70 grams of copp r sulfate per liter of water) for 25 minutesat 1 ampere and then forminutes at 4 'amperes. Next the copper-platedfoil was suspended in the polonium-containing radium D solution todeposit polonium on the copper plated foil. Said solution was maintainedat boiling temperature for 3 hours, evaporated water being replaced atfrequent intervals. Thereupon, the poloniumplated foil was removed fromthe solution, washed and dried. By means of a Geiger counter the thereonby being suspended for a short time in a nitric acid etching bath 8 thatis contained in an earthenware crock I. The foil 5 is positioned by anickel wire 8 which is secured to a stainless steel rod 9 extendingacross the mouth of the crock l. The etched foil is rinsed free of acidin water It contained in a container ll. The water rinse may berepeated, if desired, in order to remove the last traces of acid fromthe foil.

average polonium content of the foil plated by- 10 After the waterrinse, the foil 5 is ready for the this method wasfqund to be 1.42micro-micrograms, per square millimeter on measuring the alpha emissionfrom several small square samples cutfrom various parts of the foil.

Method B "inch were prepared'for receiving a plating of polonium bybeingetched to a thickness of about 0.0005 inch in nitric acid. These foils,

having a total area of 162,000 square millimeters were then immersed intheboiling solution after all of the'lead chloride had dissolved. Thepassage of steam through. the solution was continued for about 5 hoursand, in this instance,

a polonium-plating was produced on the foils having an average poloniumcontent of 3.24

plating operation which will be described hereinbelow. a

In carrying out the plating operation'I-with radioactive lead chloridewhich has not .been

previously used for plating polonium, preferably 75 pounds of the leadchloride are dissolved in 300 gallons of boiling 0.03 normalhydrochloric acid contained in a tank II, which is lined with achemically inert material, such as glass 0 ll, which does not adsorbpolonium from acid solution. The tank I2 is preferably equipped with ajacket I into which either steam or water may be introduced for heatingor cooling the contents ii of the tank; the steam entering the jacketthrough pipe l6, valve I1, and pipe ii, the condensate collecting in asuitable device such as a trap (not shown), which may suitably belocated in pipe It; or water entering through valve l9 and pipe l8 andleaving the jacket H through valve 20 and associated pipe II.

Several prepared foils 5a, 5b, 5c, 5d, etc., are suspended in theradioactive lead chloride solution l5, and the solution ismaintained atboiling temperature (approximately 100 C.) by admitmicro-micrograms persquare millimeter, when ting steam suitably at m to 15 pounds-gaugemeasured by a Geiger counter.

, Method C The preferred method for commercial plating pressure, intothe jacket ll for a plating period of about 4 to 5 hours. Valve l1 andassociated pipe it are connected to a suitable source (not of poloniumis illustrated in part by'Figures 1 40 shown) of steam, which is led tothe jacket II n and 2, and comprises, briefly, plating polonium from alead solution containing same onto a suitable base metal, cooling thesolution to precipitate lead chloride, separating the precipitated leadsalt from the mother liquor, aging said salt to-develop more polonium,and then forming a solution of the aged salt in the mother liquo'r froma previous plating operation and plating polonium as before. This methodof plating makes possible the convenient production of the maximumquantity of polonium economically available from a given amount of apolonium-producing salt by means of relatively small'and simpleapparatus.

a, covered five gallon glazed earthenware crock.

The time of aging is dependent on economic coni siderations in view' ofthe rate of increase in polonium content of the radium D, as shown inFigure 3. It may be seen that an aging period 01. several months isnecessary in order for the .polonium content to approach "the maximumvalue. Since in a commercial process platings must be made frequently,several other containers, 3, 4, etc are provided for storing variousbatches of aging lead chloride containing 70 such as radium D.

Prior to the plating operation a sheet of thin nickel foil 5 to beplated, which is about 8 inches by 36 inches by 0.003 inch, is suitablyetched to produce a better plating surface by pipe 18. Condensateforming inthe jacket I is allowed to drain through pipe I I and valveI'I into a steam trap (not shown), as has been indicated hereinabove;Mechanical agitation of 45 the solution, in addition to the agitationproduced by boiling, is unnecessary. Practically all of the availablepolonium is plated onto the foils at the end of the plating period, butno measurable lead or radium D is present on the foils. The foils arethen removed from the tank, rinsed with water and the rinsings added tothe mother liquor in the tank. After the foils are dried their poloniumcontent can be determined by means of a Geiger counter or ionizationchamber equipment.

After removal of the foils from the plating tank, steam inlet valve I1is closed and valves l9 and 20 are opened to allow cooling water to flowthrough valve l9 and pipe l8 into the Jacket II and thence through theexit valve 20 and its associated pipe 2|. The cooling water is allowedto circulate through jacket it until the temperature of the plating bathl5 has fallen preferably to about 20 0., which precipitates radium datedand set aside for aging.

In a "subsequent plating operation," the mother liquor remaining fromthe first plating operation is titrated to determine its acidity, andsufllcient acid or water is added to bring the acidity to the preferredvalue of 0.03 normal. The adjusted solution is heated to boiling andabout 50 pounds of polonium-containing radioactive lead chloride areadded thereto. The lead chloride may be taken either from a new supplyof polonium-containing radioactive lead chloride or from properly agedprecipitates of former platings, the precipitate from one plating batchdrying to about 50 pounds after aging for several months. The remainderof the subsequent plating operation is identical with the correspondingportion of the first plating operation described above.

When two plating operations were carried out in accordance with thefirst plating procedure given in Method C wherein several foils areplated in one batch, the nickel foils to be plated having a total areaof 64 square feet, two batches of plated foils were obtained showingtotal polonium contents of 21.6 and 18.8 micrograms.

A series of eightplatings carried out in accordance with the "subsequentplating operation described above produced eight batches of foils with atotal polonium content of 140.3 micrograms, each group having a poloniumcontent in the range of 15.1 to 22.6 micrograms.

No visible lead or radium D (isotope of lead) is.observed on nickelfoils plated in accordance with the preferred method, and no trace oflead is shown by spectroscopic tests.

Although other soluble radioactive lead salts, such as the acetate orbromide, may be employed in the plating process, the chloride ispreferred. If other salts are used, the corresponding acids wouldreplace the hydrochloric acid of the present preferred method. Althoughthe acidity of approximately 0.03 normal is preferred when the chlorideis used, satisfactory plating results have been obtained in the range of0.08 normal to 0.001 normal. More highly acid plating baths withacidities ranging from 0.08 normal to higher than 1.0 normal may beused, but they have the disadvantages of decreased solubility for leadchloride and increased dissolving action on the foils, when the metal ofthe latter stands higher in the electromotive series than hydrogen. Ofcourse, more than one plating tank may sometimes be an advantage. Thusit has been found that a single operator can conveniently prepare asecond plating solution in a duplicate tank and etch a second set offoils while a plating operation is going on in the first plating tank.In other words, one operator can easily carry out one plating of thesize indicated in Method C every day by the use of two plating tanks.The plating operation may be accelerated by inserting a suitable anode(not shown) in the tank 12, making the foils cathodes, and passing aweak electric current through the solution l5.

Before the polonium plated foils prepared in accordance with theinvention can be used to the best advantage commercially, the poloniummust be alloyed with other metals to form metal having a very smallpolonium content since only very small quantities of polinum need bepresent to give an alloy very desirable properties.

The alloyed metal of the invention may be made as follows:

Example 1 A 5 millimeter length of a nickel alloy wire, which had beencopper-plated and then polonium-plated in accordance with Method A, wasplaced in the positive crater of a vertical carbon are (D. C. operatedinch carbons). The carbons were then pushed together and separated. Acurrent of 20 amperes was allowed to flow for 2 to 5 seconds, at the endof which time the arc was extinguished with a high velocity stream ofnitrogen. The resulting nickelpolonium alloy pellet was filed down toone-half its thickness and a high alpha particle emission from the filedsurface was observed by means of the Geiger counter.

Example 2 A carbon crucible was made by drilling a 0.15 inch axial holein a 0.37 inch diameter carbon electrode. A 5 inch by 0.010 inch by0.062 inch nickel ribbon and a 2 inch length of 0.072 inch cylindricalnickel alloy wire were copper-plated and then polonium-plated inaccordance with Method A. The ribbon was wrapped spirally about theplated section of the wire, and. the whole was inserted in the crucible,the bottom of which was heated with a natural gas-oxygen torch. As themetal melted, the flame was moved higher on the crucible and, at thesame time, the protruding unplated length of the wire was forceddownward into the crucible. An ingot produced in this manner was foundto have a high alpha particle emission.

Example 3 As a variation of Example 2, several short lengths of heavilypolonium-plated nickel ribbons (0.010 inch by 0.062 inch) were piledinto the form of a 0.06 inch by 0.06 inch bar. The melting procedure wasthe same as that of Example 2. A ingot (0.125 inch diameter) producedwas filed down to a 0.094 inch diameter cylinder. The alpha emissionfrom the cylindrical surface of the filed ingot, which was made inaccordance with this procedure, indicated that the poloniumconcentration was about 270 micromicrograms per cubic millimeter of thenickel alloy, or about one-three hundred thousandths of one per cent.

Example 4 In this instance, the alloying efliciency of the polonium isto be measured so that measured quantities of polonium and alloyingmetal must be used. Thus polonium-plated foil having 27,090 squaremillimeters of surface containing 1.42 micro-micrograms of polonium persquare millimeter or a total of 0.0384 micrograms of polonium was meltedwith a calculated amount of nickel to produce 3,620 cubic millimeters ofa nickel-polonium alloy. The melting operation was carried out in asmall magnesium oxide crucible with an internal diameter of inch whichwas fitted into a 2 inch internal diameter graphite crucible that wasmounted in an electric induction furnace. In the melting operation, therequired amount of nickel was first heated and melted in the magnesiumoxide crucible and then the polonium-plated foil (rolled tightly into acylinder) was added to the melt. High frequency current was then allowedto pass through the melt for 20 seconds in order to insure thoroughmixing of the metals after which the current was cut off and thecrucible removed from the flirnace. An ingot about inch by inch wasobtained when the solidified alloy was removed from the magnesium oxidecrucible.

Then the ingot was hand-forged and swaged to form a cylinder of 54 inchdiameter and approximately 4 inches in length. The cylinder was nextdrawn down to 0.072 inch diameter in accordance with the usual practice.The alpha emission of thefinished wire made in accordance with thisexample was measured by means of a Geiger counter and the poloniumcontent of the wire was determined to be 8.0 micro-micrograms per cubicmillimeter of alloy. Since 10.6 micromicrograms of polonium were addedforeach cubic millimeter of nickel-polonium alloy made,

the alloying efliciency for the polonium in this case was 75 Example 5Two groups of plated foils, having a combined polonium content of 40.4micrograms, were prepared according to the first specific proceduredescribed in Method C. Applying the procedure of Example 4 (largerequipment being used) the foils were. added to sufllcient molten nickelto produce 310 pounds ofalloy. The input of polonium was-equal to 0.13microgram per pound ofalloy while the polonium per' pound of alloy wasmeasured' and found to be 0.11 microgram per pound.

It results that the alloying efflciency was 85 per a cent.

Ettample 6 Foils containing a total of 140.3 micrograms of polonium wereprepared according to the "subsequent plating procedure of Method C. Ap-85 plying. the procedure of Example 5, the foils were loys containingpolonium in the range of ap- 45.

proximately one-one hundred millionth of one per cent to one-one hundredthousandths of one percent. Obviously an alloy containing even lesspolonium, such as one billionth of one per cent or less, can bepreparedby melting the polonium-plated metal with an even larger proportion ofthe other metal. Likewise, an alloy containing a larger percentage ofpolonium than 0.00001 can be produced by melting a plated foilcontaining a larger proportion of polonium than shown by the foilsdescribed above. Although the examples show the preferred use of nickelor a nickel alloy as the non-radioactive component of the radioactivealloys produced, a similar nonradioactive metal, such as cobalt, may beused instead to produce similar alloys, no matter which radioactivemetal is chosen for the alloy. Of course, any other suitablesubstantially nonradioactive metal may also be substituted for nickel inthe method of the present invention. 05

Any workable method of forming a deposit, plating or coating of poloniumon a base metal is satisfactory for the purposes of the presentinvention. Thus, polonium may be plated by electrochemical displacementonto any other metal having a higher electrode potential than polonium(e. g., silver, copper, lead, nickel, cobalt and aluminum) although forpractical reasons metals less electropositive than aluminum arepreferred.

Polonium may also be plated onto any suitable metal electrode byelectrodeposition from a solution containing polonium. A coating ofpolonium may also be formed on a',,metal such as silver, gold orplatinum by adsorption from a solution comprising polonium. Furthermore,poloniummay be vaporized or distilledpnto another metal, preferably at asub-atmospheric pressure. These methods apply also to the production ofplatings of other radio-active metals.

In addition to spent radon tubes and the lead residues attending thepreparation of radium, other compositions containing polonium arecontemplated for use in the present method. I Some other commercialcompositions or naturally occurring compositions, which containappreciable proportions of polonium in the absence of, materialproportions of radium D or lead, are also suitable for use in obtainingpolonium for preparing radioactive metals or alloys according ,to thepresent invention. i 3 it 7 Although it is thought that .the mixtures ofmetals herein described as alloys are. pr operly so designated, it hasnot been found; possible to.

prove. .that a true alloy is always pro uced by the practice of thisinvention.- lhereiore, it is to be understood in the speci'iicationandappended claims that alloy" means anysubstantial mixture or two or moremetals. such .as the product oi the present method. Although it is othought that the radioactiv alloy produced by the method or the presentinvention is a. substantially unirorm dispersion of the radioactivemetal throughout the other components of the alloy, it is possible thatsome or the radioactive metal is oxidized during the alloying process,so that the alloy may contain a substantially unii'orm dispersion of theoxidized radioactive metal.

various modifications may be made without departing from the nature andspirit of the inyentlon as deiined in the appended claims.

What is claimed is: l. A method of separating polonium from a materialcomprising polonium and radium D,

which comprises iorming a hot slightly acid solution of material of theabove class, immersing a piece of metal in the solution, depositing thepolonium on the surface of the metal, cooling the solution toprecipitate most of the poloniumdepleted material therefrom, separatingthe precipitate from the mother liquor, aging the precipitate until morepolonium is formed, and then dissolving the aged precipitate in the hotmother liquor from a iormer depositing operation to provide a solutioncapable of depositing a further quantity of polonium onto a suitablebase metal. 1

2. A method of preparing a radioactive alloy, which comprises depositinga radioactive metal on the suriace 01' a metal to form a plated metal,

and subsequently melting the plated metal in the on the surface of ametal to form a plated metal, and adding the plated metal to moltenmetal. 4. A method of preparing a radioactive alloy,

which comprises forming a deposit of polonium on a metal from a hotslightly acid solution comprising polomum and radium D to form a platedmetal, and adding the plated metal to a calculated amount of a moltenalloying metal.

5. A method of preparing a radioactive alloy, which comprises depositinga radioactive metal on the surface of a metal to form a plated metal,

melting the plated metal, and passing a high frequency electric currenttherethrough.

6. A method of preparing a radioactive alloy, which comprises depositingpolonium on the surface of a metal to form a plated metal, melting theplated metal, and passing a high frequency electric currenttherethrough.

7. A method of preparing a polonium alloy, which comprises forming aplated foil by depositing polonium on the surface of a metal foilconsisting substantially of a material selected from the groupconsisting of copper nickel and copper-plated nickel by immersing thefoil in a hot solution comprising polonium ions, melting the plated foilin the presence of a quantity of molten metal comprising mainly nickel,and passing a high frequency electric current through the mass of metal.

8. That method of preparing a radioactive alloy comprising etching asheet of a suitable metal foil, immersing the etched metal foil in aslightly acid solution containing a radioactive metal, boiling thesolution to deposit radioactive material upon the metal foil, andthereafter melting the metal foil which has radioactive material platedthereon to form a radioactive metal alloy.

9. That method of preparing a radioactive alloy comprising preparing asheet of a suitable metal foil, immersing the prepared metal foil in asolution containing a radioactive material, boiling the solution todeposit radioactive material upon the metal foil, and thereafter addingthe metal foil which has radioactive material plated thereon to aquantity of molten metal to form a radioactive metal alloy.

10. That method of preparing a poloniumcontaining metal comprisingetching a sheet of a suitable metal foil, immersing the etched metalfoil in a polonium-containing solution, boiling the solution to depositpolonium upon the metal foil, and thereafter melting the metal foilwhich has polonium plated thereon to form poloniumcontaining metal.

11. That method of preparing a radioactive metallic wire comprisingpreparing a sheet of a suitable metal foil, immersing the prepared metalfoil in a solution containing a radioactive material, depositingradioactive material upon the metal foil, adding the metal foil whichhas radioactive material plated thereon to a quantity of molten metal toform a metal exhibiting radioactivity, and thereafter drawing the saidmetal exhibiting radioactivity down to form a radioactive metallic wire.

12. That method of preparing a metal having radioactivity comprisingpreparing a sheet of a suitable metal foil, immersing the prepared metalfoil in a solution containing a radioactive material, passing a weakelectric current through the solution and the metal foil to depositradioactive material on the metal foil, and thereafter adding the metalfoil which has radioactive material plated thereon to a quantity ofmolten metal to form a metal exhibiting radioactivity uniformlythroughout its mass.

JOHN H. DILLON.

